A number of techniques are routinely used to measure the mechanical properties of coatings and surfaces. These include, for instance, scratch testing and indentation testing. However, it is sometimes difficult to correlate results obtained from such tests with actual product performance. This is particularly the case with surfaces which are subjected to erosive wear, multiple impacts or stress-strain cycling, where surface toughness is of paramount importance.

A repetitive impact technique has been developed to enable the investigation of surfaces under such conditions. To produce multiple impacts, the specimen is oscillated such that a test probe (normally a spherical diamond) is caused to "bounce" on the specimen surface. The frequency, amplitude, normal force, oscillation angle, and diamond geometry are variable.*

For contact fatigue studies, the probe is maintained in contact with the surface, thus causing repetitive flexing and relaxing of the contact point and hence of any sub-surface layers.

The diamond amplitude is monitored vs. time. Changes in material response are indicated by variations in amplitude, which are frequently abrupt and easily recognised.

* Patents are pending for these techniques.